Excel - "The file format and extension of your file don't match" warning

Problem:

You receive this warning in Excel:

The file format and extension of "FILENAME" don't match. The file could be corrupted or unsafe. Unless you trust its source, don't open it. Do you want to open it anyway

Known product versions in scope: Office Excel 2013

Cause:

This is caused by Windows update KB5002242, and happens when opening Excel files saved on a shared drive (or other UNC path), where the total length of the path and file name exceed about 90 characters. This will affect a large number of shared drive hosted files

Resolution:

Click "Yes". The contents of your file and your ability to edit and save these files will remain unaffected.
Alternatively, shorten the overall file path to below 90 characters inclusive of the filename of your document to effectively and permanently suppress the warning.
While IT can uninstall KB5002242 from affected machines, this is a temporary fix for getting rid of the error message and it will return upon a later Windows update cycle.